High-level expression of a foreign gene from the most 3 '-proximal locus of a recombinant Newcastle disease virus

A previous report showed that insertion of a foreign gene encoding chloramp henicol acetyltransferase (CAT) between the HN and L genes of the full-leng th cDNA of a virulent Newcastle disease virus (NDV) yielded virus with grow th retardation and attenuation. The NDV vector used in that study was patho genic to chickens; it is therefore not suitable for use as a vaccine vector . In the present study, an avirulent NDV vector was generated and its poten tial to express CAT protein was evaluated. The CAT gene was under the contr ol of NDV transcriptional start and stop signals and was inserted immediate ly before the open reading frame of the viral 3'-proximal nucleocapsid prot ein gene. A recombinant NDV expressing CAT activity at a high level was rec overed. The replication and pathogenesis of the CAT-expressing recombinant NDV were not modified significantly. These results indicate the potential u tility of an avirulent NDV as a vaccine vector.